Hey Jens!
Without seeing your whole day, it's hard to know exactly what's going on. Can you post a typical day in the EASY format?
Before seeing your EASY, the only thing I can say is that 30min naps typically mean a baby is OT, however 2hrs of A time is on the low side for most 5mo. Of course given that she was premature, this may or may not affect her now. In the early days, it's a lot more important how early they were, but as they age, it makes less of a difference from what I've seen with moms of other premies. I don't have any personal experience with early babies, as mine were 1wk late and 1wk early respectively!
30min naps can also mean overstimulation. What are her A times like? How does she go to sleep - is she falling asleep independently? Use a paci?